Vacuum brake power boosters used in motor vehicles are, for instance, known from the German printed and published patent application DE-OS 37 09 172. All vacuum brake power boosters comprising a poppet valve with a rolling fold have a problem in common which is that the rolling fold is urged radially outwards due to the pressure differential acting upon it, so that the effective surface upon which the pressure differential acts is enlarged. However, the larger this surface becomes, the more the force reserve of the return force is reduced. On the other hand, however, one endeavors to maintain the difference between response force and return force as small as possible since low response forces with sufficient return forces is an objective.